1. Field of the Invention
The present invention relates to active filters, and particularly to a low frequency filter for biomedical applications.
2. Description of the Related Art
Very low frequency filters have a wide range of applications in biomedical signal processing. The bandwidth of an Electroencephalogram (EEG), for example, refers to the monitored signal due to the brain activities, and of an Electrocardiogram (ECG), which is a test for the electrical activities that are being recorded due to heart beats, are 0.1-30 Hz and 0.01-100 Hz, respectively. Amplification and pre-filtering of these signals are mandatory before further digital signal processing (DSP). However, such very low frequency filters need large passive components values, which cannot be implemented in standard analog integrated circuit (IC) fabrication. Typical values for integrated resistors are from several ohms to 40 kΩ, and for capacitors are from 0.5 pF to 50 pF. This has been a challenging design problem due to the difficulty in developing efficient methods to achieve large time constants using integrated passive elements.
Thus, a low frequency filter for biomedical applications solving the aforementioned problems is desired.